The present invention relates to the transmission of a torque between a drive pulley and a shaft driven by the pulley. A torque transmission device of this type may be used, in particular, in air-conditioning compressors such as those fitted to motor vehicles.
During the transmission of a torque between a drive pulley and a shaft driven by the pulley, and in particular in the case where a torque transmission device is used for driving an air-conditioning compressor, means for limiting the torque are generally provided, placed between the drive pulley and the driven shaft. Thus, in the event of too large a torque, resulting for example from seizing of the air-conditioning compressor, the pulley can continue to turn without driving the shaft or without slipping relative to the drive belt, which quickly leads to the destruction of this belt.
Japanese patent application JP 08-135686 uses a plurality of elastic elements squeezed between metal retaining elements as a means of torque limitation, the assembly being designed such that, in the event of too large a torque, the elastic elements escape from their normal drive position, thus eliminating torque transmission. These means are complex and therefore relatively expensive to manufacture and to assemble. In addition, they do not allow a return to torque transmission when the torque value has again become normal.
Japanese patent application JP 2000/356226 describes a torque limitation means comprising a friction system placed between the drive pulley and a coupling flange joined to the shaft of an air-conditioning compressor. The peripheral part of the coupling flange comprises on each of its faces a friction coating that cooperates on the one hand with a radial face of the pulley and on the other hand with a radial face of an annular transmission element joined to the drive pulley by a ribbed cylindrical surface. The manufacture of such a coupling flange with a double friction coating, along with the provision of a fitted transmission element, provided with ribs for joining to the pulley, proves to be complex and expensive.
Patent application WO 2005/021991 describes a rolling bearing associated with a freewheel device which comprises torque limitation means. These means consist of a friction element fitted in the freewheel support.
Patent application WO01/098678 describes a power-steering device with a screw system in which a ring gear is fitted directly onto the central portion of a shaft by means of a split annular ring comprising a plurality of bosses. Such an application is specific to a steering column, the relatively slow rotation of which makes only a few revolutions.
The subject of the present invention is a device for torque transmission between a drive pulley and a shaft rotationally driven by the pulley in which the torque limitation means are simple in structure and inexpensive to manufacture, which can easily be fitted at the shaft end, especially for a drive shaft of an air-conditioning compressor.
The subject of the present invention is also a transmission device comprising torque limitation means capable of interrupting the transmission of torque between the pulley and the driven shaft when the torque exceeds a threshold value, while allowing torque transmission to be resumed as soon as the torque value returns below this threshold value.
In one embodiment, a device for torque transmission between a drive pulley and a shaft comprises a coupling flange rotationally driven by the pulley and a hub fitted at the shaft end and rotationally joined to the shaft. Torque limitation means are fitted between the coupling flange and the hub and comprise a friction ring comprising a plurality of projecting elastic portions in friction contact with a surface of the coupling flange and/or of the hub. Thus, in the event of too large a torque between the drive pulley and the shaft, slippage intervenes and any risk of damage is avoided. As soon as the value of the torque returns below the slipping threshold, transmission takes place once again. The device is effective, simple to produce and to fit, and inexpensive.
The projecting elastic portions are preferably produced by deformation of the thin material constituting the elastic ring.
The projecting elastic portions may be undulations or bosses.
In one embodiment, the bosses occupy a central part of the friction ring, between two end parts lacking bosses.
The friction ring may be split or conversely closed.
In one embodiment, the friction ring is radially prestressed between two cylindrical bearing surfaces, the gap between which has a value less than the radial thickness of the ring.
In another embodiment, the friction ring is in the form of a flange radially prestressed between two radial surfaces, the gap between which has a value less than the axial thickness of said flange in the free state.
One or more elastic blocks may be fitted between the pulley and the coupling flange so as to damp torsional vibration.
According to another aspect, the invention also relates to an air-conditioning compressor, especially for motor vehicles, comprising a device, such as indicated above, for transmitting torque between a drive pulley and the compressor shaft.